A photonic signal processor providing finite impulse response filtering of an external input signal, the processor including: a photonic signal input having a predetermined wavelength range, a Bragg grating structure interconnected to the photonic signal input and having a series of localized modifications to the periodicity of the grating structure so as to provide a predetermined transmission output window within the stopband of the Bragg grating structure and predetermined wavelength range; a modulator interconnected to the grating structure for modulating the output from the grating structure in accordance with the external signal input; a delay structure for providing a wavelength variable delay to the output from the modulator; an intensity detector interconnected to the delay structure for determining and outputting the intensity of the delay structure output.